Testing the evolutionary sequence of high-mass protostars with CARMA

Abstract

We present 1″ resolution Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of the 3 mm continuum and 95 GHz CH3OH masers toward 14 candidate high-mass protostellar objects (HMPOs). Dust continuum emission is detected toward seven HMPOs, and CH3OH masers toward five sources. The 3 mm continuum sources have diameters <2 × 104 AU, masses between 21 and 1200 M⊙, and volume densities >108 cm-3. Most of the 3 mm continuum sources are spatially coincident with compact H ii regions and/or water masers, and are presumed to be formation sites of massive stars. A strong correlation exists between the presence of 3 mm continuum emission, 22 GHz H2O masers, and 95 GHz CH3OH masers. However, no 3 mm continuum emission is detected toward ultracompact H ii regions lacking maser emission. These results are consistent with the hypothesis that 22 GHz H2O masers and CH3OH masers are signposts of an early phase in the evolution of an HMPO before an expanding H ii region destroys the accretion disk.